[例1] 故障现象 FX120C型传真机,复印正常,但不能收发报文。 分析与检修 复印正常,不能收发报文,说明复印和收发报共用电路工作正常,故障出在调制解调器及网络控制板至外线这一范围内。根据收发报的报文信号流程(以发报为例),报文信号经调制解调器处理后,变换成模拟信号,经系统板输出后,再进行模拟量的放大处理。从该机电路可知,报文信号流经路径为:HIC3→CN23的⑿脚→CN2的⑿脚→调整发送电平→IC4(低通滤波器)→T1变压器→外线。经检查发现,CN23的⑿脚到外线间正常。故怀疑系 [Example 1] Symptom FX120C fax machine, copy normal, but can not send and receive messages. Analysis and maintenance of copy normal, can not send and receive messages, indicating that the common circuit copy and send and receive newspapers work properly, the fault lies in the modem and network control panel to the outside of this range. According to the signal process of sending and receiving message (taking the sending and receiving as an example), the signal of the message is processed by the modem and then converted into analog signal. After being output by the system board, the signal of the message is enlarged and processed by analog. From the circuit, we know that the path of the message flow through is: HIC3 → CN23 pin → CN2 pin → adjust sending level → IC4 (low pass filter) → T1 transformer → outside line. The inspection found that CN23’s feet to the normal outside. It is suspected department